A vulnerability was found which may allow a remote attacker to cause a
denial of service to Simple DNS Plus
Sending multiple  DNS respond packets to the source port of the server

This vulnerability is fixed in the new version of  Simple DNS Plus  5.1.101.

usage: sdns-dos.pl   
Exploit written by Exodus.
http://www.blackhat.org.il 

http://www.blackhat.org.il/index.php/simple-dns-plus-5041-remote-denial-of-s 
ervice-exploit/